There are problems associated with the cold forming, for example bending using a press brake, of titanium alloy sheet metal, Ti64, consisting 5.5 to 6.75 wt % aluminium, 3.5 to 4.5 wt % vanadium and the balance titanium plus incidental impurities. Ti64 has poor cold formability and the problem is one of cracking due to the slightest surface defect, even when caused by an appropriate method of handling or appropriately polished press brake tooling. Therefore, the use of Ti64 as a cold-formed sheet metal is fraught with difficulties and is liable to create components which require laboratory investigations after manufacture in order to gain confidence that there are non cracks or any other type of defect present. Such laboratory investigations extend the lead-time of the component and add considerable cost to the manufacturing process.
Due to the problem associated with cold forming of titanium alloy sheet metal consisting 5.5 to 6.75 wt % aluminium, 3.5 to 4.5 wt % vanadium and the balance titanium plus incidental impurities it has recently been common practice to use a titanium alloy sheet metal, AMS 4914, consisting 15 wt % vanadium, 3 wt % chromium, 3 wt % aluminium, 3 wt % tin and the balance titanium plus incidental impurities. AMS 4914 has good cold formability and may be heat treated after cold forming.
However, AMS 4914 is more expensive than Ti64. In addition, the heat treatment required for AMS 4914 titanium alloy sheet metal is of 8 hours duration at approximately 450° C. During this heat treatment the “stressed” formed titanium alloy sheet metal component is liable to further distortion, due to stress relaxation, which may have to be corrected after the heat treatment and thus incur further costs.